Belt driven power transmission systems are routinely used for a wide variety of applications, including automotive, agricultural, industrial, recreational and so on. The typical system comprises a toothed belt which engages a sprocket. The system allows high power transmission between the driver and the driven due to the positive mechanical engagement between the belt teeth and the sprocket grooves. Typically, the belts are subjected to a preload to assure that the teeth do not ratchet. The need for preload and proper engagement between the belt and sprocket requires that debris not be allowed to become entrapped between the belt and sprocket.
Off-road bicycles, also called mountain bikes, are used on various types of terrain in any kind of weather. In wet weather the terrain can be muddy. Mud and other debris can stick to the bike frame, tires and become entrapped in the drive train. Drive trains typically comprise chains and more recently belts.
Debris can present a problem for belt driven bikes. Mud and debris trapped between the belt and the sprocket can lead to system malfunction, belt ratcheting and premature belt failure.
Representative of the art is U.S. Pat. No. 4,805,388 (1989) which discloses a crop gathering head 10 including crop gathering belt 11, 12 of reinforced elastomeric material and its associated driving sprocket 30 and idler sheave 50 is described. The belt 11 or 12, sprocket 30 and sheave 50 system may be used to convey crops into a combine. The belt 11 or 12 includes a plurality of cleats 20 of elastomeric material on its top surface 18 and a plurality of equally spaced driving lugs 24 of elastomeric material on its bottom surface 19. The sprocket 30 has first and second sides 31, 32 respectively and comprises a plurality of equally spaced apart radially projecting teeth 33 separated by first and second cavities 34, 34′ respectively. The first cavities 34 are open only to the first side 31 of the sprocket 30. The second cavities 34′ are open only to the second side 32 of the sprocket 30. The depth D of each cavity exceeds the height H of each driving lug 24 of the belt 11 or 12 and the cavities 34, 34′ are shaped such that foreign material, for example, corn kernels, mud and ice do not clog the driving sprockets 30 and belts 11 or 12 and disable the system. Each belt 11 or 12 is also entrained about an idler sheave 50 that includes a cylindrical hub 51 having a pair of axially spaced radially projecting flanges 52, 53 respectively thereon. The inner side surfaces 54 of the flanges 52, 53 converge in a direction toward the axis of rotation 55 of the sheave 50. Each flange 52 or 53 is interrupted in the circumferential direction of the sheave 50 to provide a self-cleaning effect upon engagement with its associated belt 11 or 12.
What is needed is a debris ejecting sprocket having a cavity disposed radially inward from each groove and communicating with the groove, the cavity comprising a surface disposed at an angle (θ) with respect to an axial direction for ejecting debris. The present invention meets this need.